In this day and age of really lightweight 1P tents in the 2lb range I am seriously questioning the point of investing in a Bivy bag. Can someone explain to me why you would EVER invest in a Bivy or Bivy/Tarp combo when there are so many full 1P tents with huge space in the same weight range as a Bivy/Tarp combo?

One of the most popular reasons for tarp/bivy use is flexibility of the system. You can have a system that includes a bug bivy or net tent, a cold weather bivy, and a tarp. With this system you can cover all types of 3-season weather and some winter stuff and only bring what is needed. Careful bivy and tarp selection still beat out all but a few 1P tents in terms of weight. As far as space goes, a Gossamer Gear SpinnTwinn tarp is much larger than any solo tent, weighs about 9 oz., and you can add various bivies or bug tents for 5-10 oz. The weight for this system can be less than 20 oz. with great flexibility.

I have a highly water resistant (can withstand a brief rainstorm or plenty of snow) bivy that weighs 10 ounces. I haven't seen a tent that weighs that little (though the Lightheart Cuben gets close). This bivy packs down to the size of a 16 oz Nalgene.

I can throw this bivy down anywhere and don't need to stake it down.

In RMNP alpine areas, tents are illegal.

Of course, in general bivies are a pain to get into and out of, their breathability/stuffiness can be problematic, and, most annoying of all, when sealed up (even with the hooped pole designs) tend to make me feel like I'm going to suffocate.

One of the major advantages of a tent is in higher elevation locations where high wind is the norm not the exception. I suppose configuration of the tarp can block the wind somewhat but my point being that wind driven rain would seem to be problematic, particularly above treeline.

I have not yet bought or even used a bivy but my lighter weight tents TT and lightheart are a little breezy in winds as tarps which I have not tried either are as well so Im sure they are going to add warmth more so with wind. Im oftened tempted to try a tarp bivy combo but I bring a dog often and can see down sides with the dog

I do it simply because versatility I can plop my bivy down if the weather looks good and ditch setting up the tarp but I still have protection for my pad and bag and protection from bugs and light un forecasted rain and it allows me since my bivy has a mesh face panel I can star gaze and feel more connected to my surroundings but if I get to camp and the weather doesn't look as promising I have my tarp which also is much MUCH roomier then any one man and most two man tents that's why I use a tarp/bivy combo just my 2cents take it for what it's worth

A well pitched tarp will do just as well above treeline as a 2 lb. tent. As long as you pick a good location and have a wind shedding tarp configuration, a tarp will be just as effective if not more(depending on the situation). But there have been many times I have been above treeline with winds that would easily destroy either tarp or any 2 lb. tent....luckily having a bivy gave some protection from the elements.

And as for warmth, I wouldn't think a 2 lb. tent would add much more warmth then tarp/bivy if any. Any 2 lb. tent will likely be made out of the same materials as a tarp and bivy. Besides, I leave it to my pad and bag to keep me warm ;)

For me, it's a money thing. I can't afford any of the sub 2lb tents out there, esp. ones on the bigger side (3 person), which I'd need it I wanted to bring any of my kids along. So, I'm going the myog route- and a myog tarp and bivy is a lot easier and cheaper to make than a tent setup. I still do intent to make a 4 person mid shelter, but that's further off in the future, after I have more experience with the sewing machine.

Been using bivies for over 30 years. I have used them spring summer fall and winter. Never really thought about pros and cons, it is just what it is. Always been the minimalist type and the simplicity is what keeps me in a bivy. Still have my integral designs bivy from the late seventies. That one is bomber and has a triangle of WP material outside the netted side zip, that can be staked out and held up with a 12" pole or stick. A great design that can keep your pack or other small area dry. Got me thinking that someone should MYOG this design.

I think you will find that there is no one perfect shelter solution for every situation.

With all things UL, it is about trade offs.

Yes, the bivy and tarp that I use gives me a lot of flexibiilty and a different way to experience sleeping outdoors.

Think it would be hard to argue about a free standing tent's advantages above treeline over a tarp and bivy in bad weather.

To me, UL is about hyper speciallization....I have the gear/tools to carry exactly the combination of gear that I think is necessary for the trip at hand. The hyperspeicalization of going UL might give me a smaller margin of error if the weather turns bad or if it rains, but I am making those decisions for myself...risk vs. reward of a lighter pack.

That said, I have weathers a pretty nasty storm on Mt. Whitney above treeline that put everyone's shelters to the test and my MLD poncho tarp stood strong the whole night, where other tents had rain flys ripped off. (All about having huge piles of rock on your stakes and a tight pitch on your tarp).

"but no matter how big the tarp is... if you are using the bivy... the size is very constricted right?

Or are you guys saying that you set up one or the other?

where do you change, or how do you remove layers or add layers in the middle of the night?"

My bivy is nothing more than a "sleeping bag cover. So to answer the questions above..... the exact same way you would if you were just using your sleeping bag.

One of the biggest advantages to a bivy is that it will block the wind if you are using a quilt eliminating the drafts. The bivy allows you to comfortably use a quilt and eliminate the ground cover. I also pack my quilt in it so it also serves as a pack liner in all but the most demanding trips.

I really appreciate the very thoughtful feedback on the topic. For the most part I think the Bivy and Tarp kinda go hand in hand and so you can't really talk about one without the other.

I have migrated from traditional backpacking tents to ultralight trekking pole tents and now to consideration of a Bivy/Tarp combination. I suppose that's the natural evolution of someone going down the path of trimming ounces and sometimes lbs from their setup. I can see where some creativity in the pitch and location of your Tarp can go a long ways in providing an excellent shelter in even the worst conditions.